using SRAM state as a source of randomness

[Alexander Klimov]

Hi.

On Sun, 16 Sep 2007, Joachim Strmbergson wrote:
> One could add test functionality that checks the randomness of the
> initial SRAM state after power on. But somehow I don't think a good test
> suite and extremely low cost devices (for example RFID chips) are very
> compatible concepts.

One can test a source of randomness by checking statistics of its few
samples, but if I understand the article correctly, in case of SRAM
each cell behaves as an independent source of randomness: some bits
are almost always stuck at fixed values while others have some
freedom. In this case it is pointless to do tests using initial SRAM
state after a single power on, because to gather a few samples from
each source one needs to repeatedly reset the device.

Applying statistical tests to a hash of the whole SRAM does not make
much sense either -- a good hash function will give statistically good
results even if you give it a counter.

-- 
Regards,
ASK

---------------------------------------------------------------------
The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at metzdowd.com